Multicast refers to the technology to deliver same data from one or more sources to many destinations. Depending on the number of sources in a session, multicast can be one-to-many or many-to-many. When disseminating data to multiple destinations, a source may establish separate unicast sessions to these destinations respectively. However, scalability and efficiency issues arise. Some data may have to be transmitted along certain network links many times. Thus, a multicast approach addresses these issues.
Multicast is a network layer service, which enables applications to disseminate data and information among multiple destinations efficiently. Network layer devices (usually, the routers) either forward multicast packets along pre-computed paths, or use multicast routing protocols to establish multicast paths (such as in IPv4, the DVMRP, MOSPF, PIM protocols). Although there were already quite a few works on network multicasting, such as the ST protocol, IP multicast thrives after Deering's pioneering works. Deering's IP multicast model includes an architecture of multicast groups, and protocols supporting layer-3 functions, such as membership management and routing. In a local area network, a host may use IGMP to announce its membership requests to join certain multicast groups and communicate with local routers and other hosts. Routers listen to IGMP messages to learn local membership information. With certain routing protocols, multicast packets can be forwarded across subnets.
Multicast routing protocols experienced several stages of protocol development. At first, protocols were developed to accommodate existing unicast protocols, such as RIP or OSPF. Respective protocols are DVMRP, and MOSPF. These protocols have been implemented in most of the routing and layer-3 products. For reasons such as scalability in wide area networks, routing protocols that build shared trees for a whole multicast group have been proposed after the above protocols that are based on source-rooted trees. CBT and PIM are such representative protocols. However, these routing protocols are basically best-effort. In other words, oblivious to quality of service (QoS) concerns. When taking QoS into consideration, constraints such as bandwidth and delay should be applied. The problem is usually termed as the constrained Steiner minimum tree problem. The basic idea is to find an unconstrained shortest path tree (SPT) first. If the end-to-end delay to any group member violates the delay bound, path from the source to that group member is replaced by a path with the least delay.
When a network has a large amount of multicast sessions as its main application traffic, there are many issues need to be addressed, including path management, fault tolerance, routing performance and QoS. The present invention address network resource management for such systems. The present invention focuses on path management which accounts for bandwidth constraints in multicast-intensive packet-based media delivery system, such as an IP-based surveillance network. In addition, the path management approach will minimize global bandwidth utilization for the network.